This invention relates to methods of making fast-setting bonded aggregate structures, having utility for various purposes for which concrete and conventional refractories are employed, by mixing an aggregate containing magnesia with ammonium phosphates in aqueous solution. In an important specific aspect, the invention is particularly directed to the production of fast-setting, phosphate-bonded, magnesia-containing aggregate structures having utility as concretes e.g. for outdoor load-bearing use.
It has heretofore been known that fast-setting structures having advantageous properties for diverse uses can be produced by mixing, with a magnesia-containing aggregate, ammonium phosphates in aqueous solution, provided that the composition of the phosphates is at least about 60% by weight pyrophosphate and higher polyphosphates. U.S. Pat. No. 3,879,209 describes a method of producing a concrete structure by establishing such a mixture, introducing it to a form defining a shaped open space, and allowing it to set for an extended period at ambient atmospheric temperature. The structure thus produced progressively develops hydraulic strength, forms a strong bond with existing concrete or other surfaces, and has low porosity, so as to be capable of outdoor load-bearing use e.g. for paving or repairing roadways. U.S. Pat. Nos. 3,285,758 and 3,413,385 describe methods of making or repairing refractory linings or walls with such mixtures, wherein the produced structure develops high porosity (as desired for thermal insulation) by exposure to elevated temperature during or shortly after application of the mixture.
The mixtures employed in the methods of the aforementioned patents set, and develop usable strength, much more rapidly than conventional materials. Nonetheless, for some purposes, even faster setting times and higher early strengths (i.e. strength developed within at most a few hours of setting) would be desirable. For instance, in the repair of concrete sea walls exposed only at low tide, it would be desirable to use a patching composition that sets and develops substantial strength within a single period of exposure of the wall. Again, for road repairs, accelerated development of strength of a path would advantageously shorten the time during which the patched roadway must be kept out of service.